The present invention relates to a wholly aromatic polyester and to a production process therefor. More specifically, it relates to an amorphous wholly aromatic polyester which is excellent in heat resistance, toughness, mechanical properties and yet color and to a process for producing the same efficiently.
Higher properties have recently been required of engineering plastics which have high heat resistance and excellent mechanical strength. Amorphous engineering plastics include aromatic polyester carbonates and wholly aromatic polyesters derived from aromatic diols and aromatic dicarboxylic acids. For example, a wholly aromatic polyester which comprises 2,2-bis(4-hydroxyphenyl)propane (to be referred to as bisphenol A hereinafter) as an aromatic diol and terephthalic acid and isophthalic acid as aromatic dicarboxylic acids has relatively well balanced properties and is used for various purposes.
Studies have been made on processes for producing these amorphous wholly aromatic polyesters, out of which an interfacial polycondensation process between an acid halide of an aromatic dicarboxylic acid and an aromatic diol has already been industrialized. However, methylene chloride which is generally used as a reaction solvent in this interfacial polycondensation process is a chemical substance which has environmental and hygienic problems and whose handling needs much attention. Since its boiling point is very low at 40xc2x0 C., it is difficult and costs dear to construct a closed system capable of completely recycling methylene chloride used in the production of an aromatic polyester.
The production of an aromatic polyester carbonate from an acid halide of an aromatic dicarboxylic acid, aromatic diol and phosgene by an interfacial polymerization process involves similar problems. Then, a melt polymerization process for these polymers is now under investigation.
However, when these polymers are to be directly obtained from an aromatic dicarboxylic acid and an aromatic diol by the melt polymerization process, coloring occurs markedly and the polymerization rate is low. Therefore, the process is not practical. In fact, there are known other processes such as (1) one in which a diaryl ester of a dicarboxylic acid and a diol are reacted with each other, (2) one in which a dicarboxylic acid and a lower aliphatic carboxylate of a diol are reacted with each other, and (3) one in which a lower aliphatic carboxylic anhydride is added when a dicarboxylic acid and a diol are reacted with each other as a modification of the process (2). However, the processes (1) and (2) involve such a problem that raw materials must be esterified in advance, thereby boosting costs. The processes (2) and (3) have such problems that the apparatuses are easily corroded by a lower aliphatic carboxylic acid formed during a reaction and that the obtained polymer has a large content of terminal COOH group.
As means of solving the above problems, there is a process in which an aromatic dicarboxylic acid, aromatic diol and diaryl carbonate are reacted with one another. Even with this process, it is difficult to obtain a polymer which is excellent in color. As means of improving color, JP-A 3-128926 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d) discloses a process for producing an aromatic polyester by reacting an aromatic dicarboxylic acid, aromatic diol and diaryl carbonate in the presence of a boron-tertiary amine complex compound and/or a quaternary ammonium borohydride compound as a catalyst. JP-A 4-236224 discloses a process for producing an aromatic polyester in the presence of a specific tin compound as a catalyst.
Generally speaking, aromatic dicarboxylic acids have low solubility and the dissolution of an aromatic dicarboxylic acid is rate-determined step in the polymerization reaction. Therefore, a reaction must be carried out at a high temperature and may take long, whereby there is limitation to the improvement of color. In the conventional melt polymerization process, a sublimate is formed during a polymerization reaction, thereby making the production process complicated due to the removal of the sublimate and equipment bulky with the result of a rise in costs.
To solve the above problems, some of the inventors of the present invention disclosed in JP-A 7-133345 that a wholly aromatic polyester which is excellent in color and contains an extremely small amount of a sublimate formed during a polymerization reaction can be produced by reacting an aromatic dicarboxylic acid, aromatic diol and diaryl carbonate in the presence of a specific pyridine compound.
However, a wholly aromatic polyester having a higher degree of polymerization is now in demand along with the improvement of required properties and a process for obtaining a wholly aromatic polyester having a high degree of polymerization in a short period of time is desired.
It is an object of the present invention to provide a process for producing a wholly aromatic polyester directly from a dicarboxylic acid and a diol by melt polymerization on an industrial scale at a low cost in a short period of time without esterifying the dicarboxylic acid or diol in advance.
It is another object of the present invention to provide a wholly aromatic polyester which is excellent in heat resistance, toughness, mechanical properties and color and has a high degree of polymerization.
Other objects and advantages of the present invention will become apparent from the following description.
Firstly, according to the present invention, the above objects and advantages of the present invention are attained by a process for producing a wholly aromatic polyester comprising melt polycondensing by heating an aromatic dicarboxylic acid represented by the following formula (I):
HOOCxe2x80x94A1xe2x80x94COOHxe2x80x83xe2x80x83(I)
wherein A1 is a substituted or unsubstituted divalent aromatic group having 6 to 20 carbon atoms, an aromatic diol represented by the following formula (II):
HOxe2x80x94A2xe2x80x94Xxe2x80x94A3xe2x80x94OHxe2x80x83xe2x80x83(II)
wherein A2 and A3 are each independently a substituted or unsubstituted phenylene group, and X is a group represented by the following formula: 
wherein R1, R2, R3 and R4 are each independently a hydrogen atom, halogen atom, alkyl group having 1 to 6 carbon atoms, cycloalkyl group having 5 to 6 carbon atoms, aryl group having 6 to 12 carbon atoms or aralkyl group having 7 to 12 carbon atoms, and q is an integer of 4 to 10, with the proviso that R3""s and R4""s may be the same or different, and a diaryl carbonate in the presence of at least one catalyst selected from the group consisting of (a) a combination of a pyridine compound represented by the following formula (III): 
wherein R5 and R6 are each independently a hydrogen atom, alkyl group having 1 to 6 carbon atoms, cycloalkyl group having 5 to 10 carbon atoms, aryl group having 6 to 12 carbon atoms or aralkyl group having 7 to 12 carbon atoms, or R5 and R6 together with a nitrogen atom bonded thereto may be bonded together to form a 5- to 7-membered ring, R7 is an alkyl group having 1 to 6 carbon atoms, cycloalkyl group having 5 to 10 carbon atoms, aryl group having 6 to 12 carbon atoms or aralkyl group having 7 to 12 carbon atoms, and n is an integer of 0 to 4, with the proviso that when n is an integer of 2 to 4, R7""s may be the same or different, and an alkali metal carbonate or an alkali metal bicarbonate, (b) a combination of a pyridine compound represented by the above formula (III) and an organic tin compound represented by the following formula (IV): 
wherein R8 is an alkyl group having 1 to 20 carbon atoms, or unsubstituted or substituted aryl group having 6 to 20 carbon atoms, R9 is an alkyl group having 1 to 20 carbon atoms, or unsubstituted or substituted aryl group having 6 to 20 carbon atoms, R10 is a single bond, alkylene group having 1 to 10 carbon atoms, or unsubstituted or substituted arylene group having 6 to 20 carbon atoms, and p+r+2s=2 or 4, with the proviso that when p+r+2s=2, p=0 or 1, r=0,1 or 2 and s=0 or 1, and when p+r+2s=4, p is an integer of 0 to 3, r is an integer of 0 to 4 and s is an integer of 0 to 2, and (c) an organic titanium compound represented by the following formula (V):
Ti(OR11)4xe2x80x83xe2x80x83(V)
wherein R11 is an alkyl group having 1 to 6 carbon atoms, cycloalkyl group having 5 to 10 carbon atoms, aralkyl group having 7 to 12 carbon atoms or aryl group having 6 to 12 carbon atoms, with the proviso that R11""s may be the same or different.
Secondly, according to the present invention, the above objects and advantages of the present invention are attained by a wholly aromatic polyester which contains a recurring unit represented by the following formula (A): 
wherein A1, A2, A3 and X are as defined hereinabove, and which has a haze value of 15 or less when it is molded into a 2 mm thick plate and an increase in haze value of 50 or less when this molded plate is immersed in water heated at 120xc2x0 C. for 100 hours.